Clostridium botulinumDr.T.V.Rao MD

Clostridium botulinum

• Clostridium botulinum is a Gram-positive, rod-shaped bacterium that produces several toxins. The best known are its neurotoxins, subdivided in types A-G, that cause the flaccid muscular paralysis seen in botulism. They are also the main paralytic agent in botox. C. botulinum is an anaerobic spore-former, which produces oval, sub terminal endospores and is commonly found in soil.

Characters of C.botulinum• A gram-positive, anaerobic

bacilli.• Spore forming.• Toxin forming. • Heat sensitive.• Prefers low acid environment.• Cause Botulism disease.

Botulism- Microbiology• Toxin produced by the

bacterium Clostridium botulinum

• Anaerobic, gram positive, rod-shaped bacteria

• Bacteria are 0.5 to 2.0 mcm in width and 1.6 to 22.0 mcm in length

• Create spores that can remain dormant for 30 years or more

• Spores extremely resistant to environmental stressors, such as heat and UV light

C. botulinum

MicrobiologyC. Botulinum

– Gram-positive obligate anaerobic bacillus

– Spore-forming – Produces botulinum

toxin– Heat sensitive as

bacillus– Prefers low acid

environmentInglesby, T. The Washington Post

Wednesday, December 9, 1998; Page H01

Toxins • liberated during growth. • Seven types of toxins (A-G). • Antigenic (light and heavy chain).• Environmental survival. (Inactivated by

heat 100ºC for 20min ).• Most potential biological warfare

agents.• Lethal dose= 1-2 g .

Neurotoxin types• Neurotoxin types production is the unifying feature of the

species C. botulinum. Seven types of toxins have been identified and allocated a letter (A-G). Most strains produce one type of neurotoxin but strains producing multiple toxins have been described. The toxin type has been designated Bf as the type B toxin was found in excess to the type F. Similarly, strains producing Ab and Af toxins have been reported. There is evidence that the neurotoxin genes have been the subject of horizontal gene transfer, possibly from a viral source. This theory is supported by the presence of integration sites flanking the toxin in some strains of C. botulinum. However, these integrations sites are degraded indicating that the C. botulinum acquired the toxin genes quite far into the evolutionary past. ( Wikipedia )

Toxins• Botulinum toxin is synthesized as a single

polypeptide chain ( low potency).• The toxin is nicked by a bacterial protease (or by

gastric proteases) to produce two chains : a light chain (the A fragment) a heavy chain (the B fragment)

connected by a disulfide bond.• The A fragment of the nicked toxin, becomes

the most potent toxin found in nature

Toxins• Absorbed in GIT, blood, peripheral

neuromuscular synapse.• Presynaptic block Acetylcholine release

(by proteolysis of SNARE proteins in neuron which is important in Ach release) muscle paralysis.

• SNARE proteins are synaptobrevin, SNAP-25 and syntaxin.

Pathogenesis• Transmitted in three ways:

– Food or water toxin contamination.– Wound infected with C. Botulinum.– Ingestion of C. botulinum.

• Most common contaminated food: Vacuum packed, or canned alkaline food.

E.g. fish, green beans, any home-canned food.• Foods eaten without cooking.

Pathogenesis of Infant Botulism

• Cause :infection by C. botulinum.• Age: 5 - 20 weeks of age.• Characterized by constipation and weak

sucking.• It cause “sudden infant death

syndrome-SIDS”.• found in the stool.

Pathogenesis• Toxin must enter body

– Direct toxin absorption from mucosal surface• Gut – foodborne• Lungs – inhalational

– Via toxin produced by infection with C.botulinum• Skin breaks – wound botulism after trauma, IV drugs• Gut – intestinal botulism• Would not be seen in BT event, as toxin would be used

• Does not penetrate intact skin

Pathogenesis• Estimated lethal

human dose• crystalline type

A toxin• 0.09-0.15 g

given iv or im• 0.70-0.90 g

inhalationally• 70 g given po

Symptoms• Appear in 18-24 hrs.• include : Blurry vision, Double vision. Dry mouth. Trouble swallowing. Trouble breathing. Muscle weakness.Fever is not a symptom of botulism

Clinical Features• Classic Triad

– Symmetric, descending flaccid paralysis with prominent bulbar palsies

– Afebrile – Clear sensorium

• Bulbar palsies summarized as "4 Ds"– Diplopia, dysarthria, dysphonia, dysphagia

Botulism symptoms: Characteristic Triad

• Symmetric, descending (cranial nerves first, then upper extremities, then respiratory muscles, and lower extremities) flaccid paralysis with prominent bulbar palsies, particularly:– Diplopia – double vision– Dysarthria – difficulty in speech articulation– Dysphonia – difficulty in voice production– Dysphagia – difficulty in swallowing

• Patient is afebrile (although fever may be present in wound botulism)

• Patient’s sensibilities intact; cognitive functions unaffected

Signs of Food-borne and Wound Botulism

• Ventilatory (respiratory) problems

• Eye muscle paresis/paralysis (extra ocular, eyelid)

• Dry mucous membranes in mouth/throat

• Dilated, fixed pupils• Ataxia• Hypotension• Nystagmus• Decreased to absent deep

tendon reflexes

A. Patient at rest. Note bilateral mild ptosis, dilated pupils, disconjugate gaze, and symmetric facial muscles.B, Patient was requested to perform his maximum smile. Note absent smile creases, ptosis, minimally asymmetric smile.

Diagnostic laboratory test

• Toxins found in serum, leftover food.

• Mice injected with toxin die rapidly.• In infants, found in stool.

Brain scan, spinal fluid examination, nerve conduction test.

Diagnosis• Clinical diagnosis• Diagnostic tests help confirm

–Toxin neutralization mouse bioassay • Serum, stool, or suspect foods

– Infant botulism • C botulinum organism or toxin in feces• Testing is done in Reference laboratories

under Biosafety regulations

Treatment

• Trivalent (A,B,E) antitoxin must administrated intravenously (recovery takes several weeks)

• Mechanical respirator is administrated if necessary.

Treatment• Antitoxin action

– Food-borne botulism• Neutralizing antibody levels exceed toxin levels• Single dose adequate

– Large exposure (e.g. biological weapon)• can confirm adequacy of neutralization

– recheck toxin levels after treatment

• Antitoxin adverse effects– Serum sickness (2-9%), anaphylaxis (2%)

Prevention• Natural disease

–Boil home-canned foods 10 minutes–Follow USDA instructions on home-

canning–Restrict honey from < 1 year old–Seek medical care for wounds –Avoid injectable street drugs

• Programme Created by Dr.T.V.Rao MD for Medical and Health Care

Professionals in the Developing World• Email

• doctortvrao@gmail.com

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